An Unprecedented Effective Enzymatic Carboxylation of Phenols

CO2 Fixation into Useful Aromatic Carboxylic Acids via C (sp2)-X Bonds Functionalization

Carbon dioxide (CO2) is an abundant and readily available carbon source. Its transformation into high-added-value chemicals is a beneficial strategy, which mitigates greenhouse gas emissions and provides new raw material sources for the chemical industry. Among these chemicals, the aromatic carboxylic acids and derivatives have broad applications in medicine, pesticides, and materials science. Therefore, the carboxylation of C(sp2)-X (X = metal, halide, H, O, or S) bonds with CO2 to efficiently construct aromatic carboxylic acids and their derivatives is a synthetic strategy of significance. This review highlights the recent progress in constructing carboxylic acids and derivatives through the carboxylation of C(sp2)-X bonds with CO2 including literature published from 2000 to December 2024.

Tutorial Review on the Set-Up and Running of Quantum Mechanical Cluster Models for Enzymatic Reaction Mechanisms

Enzymes turnover substrates into products with amazing efficiency and selectivity and as such have great potential for use in biotechnology and pharmaceutical applications. However, details of their catalytic cycles and the origins surrounding the regio- and chemoselectivity of enzymatic reaction processes remain unknown, which makes the engineering of enzymes and their use in biotechnology challenging. Computational modelling can assist experimental work in the field and establish the factors that influence the reaction rates and the product distributions. A popular approach in modelling is the use of quantum mechanical cluster models of enzymes that take the first- and second coordination sphere of the enzyme active site into consideration. These QM cluster models are widely applied but often the results obtained are dependent on model choice and model selection. Herein, we show that QM cluster models can give highly accurate results that reproduce experimental product distributions and free energies of activation within several kcal mol-1, regarded that large cluster models with >300 atoms are used that include key hydrogen bonding interactions and charged residues. In this tutorial review, we give general guidelines on the set-up and applications of the QM cluster method and discuss its accuracy and reproducibility. Finally, several representative QM cluster model examples on metal-containing enzymes are presented, which highlight the strength of the approach.

A pushed biosynthesis of 2,6-dihydroxybenzoic acid by the recombinant 2,3-dihydroxybenzoic acid decarboxylase immobilized on novel amino-modified lignin-containing cellulose nanocrystal aerogel

Production of 2,6-dihydroxybenzoic acid (2,6-DHBA) via enzymatic carboxylation of resorcinol by decarboxylases is of great promising but shows depressed equilibrium conversion. In this study, 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus oryzae (2,3-DHBD_Ao) pushing the conversion towards carboxylation for efficient 2,6-DHBA biosynthesis was achieved. Meanwhile, a novel amino-modified and lignin-doped cellulose nanocrystal aerogel (A-LCNCA) with high specific surface area and prominent CO2 capture was prepared for 2,3-DHBD_Ao immobilization. 2,3-DHBD_Ao@A-LCNC contributed a further enhanced conversion of carboxylation with the maximal conversion of 76.2 %, which was correlated to both the activity of 2,3-DHBD_Ao and the high CO2 loading capacity of A-LCNCA. Moreover, 2,3-DHBD_Ao@A-LCNC exhibited superior performances in a wider range of temperature and higher concentrations of substrate, with a prolonged storage period longer than 30 days. After seven cycles reuse, 2,3-DHBD_Ao@A-LCNCA could retain 85.3 % of its original activity. These results suggest a considerable potential of 2,3-DHBD_Ao@A-LCNCA in the selective biosynthesis of 2,6-DHBA.

Enzymatic Carboxylation of Resorcinol in Aqueous Triethanolamine at Elevated CO2 Pressure

The fixation of CO2 by enzymatic carboxylation for production of valuable carboxylic acids is one way to recycle carbon. Unfortunately, this type of reaction is limited by an unfavourable thermodynamic equilibrium. An excess of the C1 substrate is required to increase conversions. Solvents with a high CO2 solubility, such as amines, can provide the C1 substrate in excess. Here, we report on the effect of CO2 pressures up to 1100 kPa on the enzymatic carboxylation of resorcinol in aqueous triethanolamine. Equilibrium yields correlate to the bicarbonate concentration. However, inhibition is observed at elevated pressure, severely reducing the enzyme activity. The reaction yields were reduced at higher pressures, whereas at ambient pressure, higher yields were achieved. Overall, CO2 pressures above 100 kPa have been demonstrated to be counterproductive for improving the biotransformation, as productivity decreases rapidly for only a modest improvement in conversion. It is expected that CO2 carbamylation intensifies at elevated CO2 pressures, causing the inhibition of the enzyme. To further increase the reaction yield, the in situ product precipitation is tested by the addition of the quaternary ammonium salt tetrabutylammonium bromide.

De novo biosynthesis of 2-hydroxyterephthalic acid, the monomer for high-performance hydroxyl modified PBO fiber, by enzymatic Kolbe-Schmitt reaction with CO2 fixation

BACKGROUND

High-performance poly(p-phenylenebenzobisoxazole) (PBO) fiber, with excellent mechanical properties (stiffness, strength, and toughness), high thermal stability combined and light weight, are widely employed in automotive and aerospace composites, body armor and sports goods. Hydroxyl modified PBO (HPBO) fiber shows better photostability and interfacial shear strength. 2-Hydroxyterephthalic acid (2-HTA), the monomer for the HPBO fiber, is usually synthesized by chemical method, which has poor space selectivity and high energy consumption. The enzymatic Kolbe-Schmitt reaction, which carboxylates phenolic substrates to generate hydroxybenzoic acids with bicarbonate/CO2, was applied in de novo biosynthesis of 2-HTA with CO2 fixation.

RESULTS

The biosynthesis of 2-HTA was achieved by the innovative application of hydroxybenzoic acid (de)carboxylases to carboxylation of 3-hydroxybenzoic acid (3-HBA) at the para-position of the benzene carboxyl group, known as enzymatic Kolbe-Schmitt reaction. 2,3-Dihydroxybenzoic acid decarboxylase from Aspergillus oryzae (2,3-DHBD_Ao) were expressed in recombinant E. coli and showed highest activity. The yield of 2-HTA was 108.97 ± 2.21 μg/L/mg protein in the whole-cell catalysis. In addition, two amino acid substitutions, F27G and T62A, proved to be of great help in improving 2,3-DHBD activity. The double site mutation F27G/T62A increased the production of 2-HTA in the whole-cell catalysis by 24.7-fold, reaching 2.69 ± 0.029 mg/L/mg protein. Moreover, de novo biosynthetic pathway of 2-HTA was constructed by co-expression of 2,3-DHBD_Ao and 3-hydroxybenzoate synthase Hyg5 in S. cerevisiae S288C with Ura3, Aro7 and Trp3 knockout. The engineered strain synthesized 45.40 ± 0.28 μg/L 2-HTA at 36 h in the CO2 environment.

CONCLUSIONS

De novo synthesis of 2-HTA has been achieved, using glucose as a raw material to generate shikimic acid, chorismic acid, and 3-HBA, and finally 2-HTA. We demonstrate the strong potential of hydroxybenzoate (de)carboxylase to produce terephthalic acid and its derivatives with CO2 fixation.

Enzymatic Conversion of CO2: From Natural to Artificial Utilization

Enzymatic carbon dioxide fixation is one of the most important metabolic reactions as it allows the capture of inorganic carbon from the atmosphere and its conversion into organic biomass. However, due to the often unfavorable thermodynamics and the difficulties associated with the utilization of CO2, a gaseous substrate that is found in comparatively low concentrations in the atmosphere, such reactions remain challenging for biotechnological applications. Nature has tackled these problems by evolution of dedicated CO2-fixing enzymes, i.e., carboxylases, and embedding them in complex metabolic pathways. Biotechnology employs such carboxylating and decarboxylating enzymes for the carboxylation of aromatic and aliphatic substrates either by embedding them into more complex reaction cascades or by shifting the reaction equilibrium via reaction engineering. This review aims to provide an overview of natural CO2-fixing enzymes and their mechanistic similarities. We also discuss biocatalytic applications of carboxylases and decarboxylases for the synthesis of valuable products and provide a separate summary of strategies to improve the efficiency of such processes. We briefly summarize natural CO2 fixation pathways, provide a roadmap for the design and implementation of artificial carbon fixation pathways, and highlight examples of biocatalytic cascades involving carboxylases. Additionally, we suggest that biochemical utilization of reduced CO2 derivates, such as formate or methanol, represents a suitable alternative to direct use of CO2 and provide several examples. Our discussion closes with a techno-economic perspective on enzymatic CO2 fixation and its potential to reduce CO2 emissions.

Crystallization-based downstream processing of ω-transaminase- and amine dehydrogenase-catalyzed reactions

This study highlights the use of selective crystallization as a downstream-processing concept for amine products from biocatalytic reactions.

Immobilization of carbonic anhydrase for CO2 capture and utilization

Carbonic anhydrase (CA) is an excellent candidate for novel biocatalytic processes based on the capture and utilization of CO₂. The setup of efficient methods for enzyme immobilization makes CA utilization in continuous bioreactors increasingly attractive and opens up new opportunities for the industrial use of CA. The development of efficient processes for CO₂ capture and utilization (CCU) is one of the most challenging targets of modern chemical reaction engineering. In the general frame of CCU processes, the interest in the utilization of immobilized CA as a biocatalyst for augmentation of CO₂ reactive absorption has grown consistently over the last decade. The present mini-review surveys and discusses key methodologies for CA immobilization aimed at the development of heterogeneous biocatalysts for CCU. Advantages and drawbacks of covalent attachment on fine granular solids, immobilization as cross-linked enzyme aggregates, and "in vivo" immobilization methods are presented. In particular, criteria for optimal selection of CA-biocatalyst and design of CO₂ absorption units are presented and discussed to highlight the most effective solutions. Perspectives on biocatalytic CCU processes that can include the use of CA in an enzymatic reactive CO₂ absorption step are eventually presented with a special focus on two examples of CO₂ fixation pathways: hybrid enzyme-microalgae process and enzyme cascade for the production of carboxylic acids. KEY POINTS: • Covalent immobilization techniques applied to CA are effective for CO₂ ERA. • Biocatalyst type and morphology must be selected considering CO₂ ERA conditions. • Immobilized CA can offer novel routes to CO₂ capture and direct utilization.

Structural Basis of Salicylic Acid Decarboxylase Reveals a Unique Substrate Recognition Mode and Access Channel

Salicylic acid (SA) decarboxylase from Trichosporon moniliiforme (TmSdc), which reversibly catalyses the decarboxylation of SA to yield phenol, is of significant interest because of its potential for the production of benzoic acid derivatives under environmentally friendly reaction conditions. TmSdc showed a preference for C2 hydroxybenzoate derivatives, with k_cat/K_m of SA being 3.2 × 10³ M^-1 s^-1. Here, we presented the first crystal structures of TmSdc, including a complex with SA. The three conserved residues of Glu8, His169, and Asp298 are the catalytic residues within the TIM-barrel domain of TmSdc. Trp239 forms a unique hydrophobic recognition site by interacting with the phenyl ring of SA, while Arg235 is responsible for recognizing the hydroxyl group at the C2 of SA via hydrogen bond interactions. Using a semi-rational combinatorial active-site saturation test, we obtained the TmSdc mutant MT3 (Y64T/P191G/F195V/E302D), which exhibited a 26.4-fold increase in k_cat/K_m with SA, reaching 8.4 × 10⁴ M^-1 s^-1. Steered molecular dynamics simulations suggested that the structural changes in MT3 relieved the steric hindrance within the substrate access channel and enlarged the substrate-binding pocket, leading to the increased activity by improving substrate access. Our data elucidate the unique substrate recognition mode and the substrate entrance tunnel of SA decarboxylase.

Cell-free chemoenzymatic starch synthesis from carbon dioxide

[Figure: see text].

Mechanisms of metal-dependent non-redox decarboxylases from quantum chemical calculations

Quantum chemical calculations are today an extremely valuable tool for studying enzymatic reaction mechanisms. In this mini-review, we summarize our recent work on several metal-dependent decarboxylases, where we used the so-called cluster approach to decipher the details of the reaction mechanisms, including elucidation of the identity of the metal cofactors and the origins of substrate specificity.

Decarboxylases are of growing potential for biocatalytic applications, as they can be used in the synthesis of novel compounds of, e.g., pharmaceutical interest. They can also be employed in the reverse direction, providing a strategy to synthesize value‐added chemicals by CO₂ fixation. A number of non-redox metal-dependent decarboxylases from the amidohydrolase superfamily have been demonstrated to have promiscuous carboxylation activities and have attracted great attention in the recent years. The computational mechanistic studies provide insights that are important for the further modification and utilization of these enzymes in industrial processes. The discussed enzymes are: 5‐carboxyvanillate decarboxylase, γ‐resorcylate decarboxylase, 2,3‐dihydroxybenzoic acid decarboxylase, and iso-orotate decarboxylase.

Synthetic Enzyme-Catalyzed CO2 Fixation Reactions

In recent years, (de)carboxylases that catalyze reversible (de)carboxylation have been targeted for application as carboxylation catalysts. This has led to the development of proof-of-concept (bio)synthetic CO2 fixation routes for chemical production. However, further progress towards industrial application has been hampered by the thermodynamic constraint that accompanies fixing CO2 to organic molecules. In this Review, biocatalytic carboxylation methods are discussed with emphases on the diverse strategies devised to alleviate the inherent thermodynamic constraints and their application in synthetic CO2 -fixation cascades.

Metal Ion Promiscuity and Structure of 2,3-Dihydroxybenzoic Acid Decarboxylase of Aspergillus oryzae

Broad substrate tolerance and excellent regioselectivity, as well as independence from sensitive cofactors have established benzoic acid decarboxylases from microbial sources as efficient biocatalysts. Robustness under process conditions makes them particularly attractive for preparative-scale applications. The divalent metal-dependent enzymes are capable of catalyzing the reversible non-oxidative (de)carboxylation of a variety of electron-rich (hetero)aromatic substrates analogously to the chemical Kolbe-Schmitt reaction. Elemental mass spectrometry supported by crystal structure elucidation and quantum chemical calculations verified the presence of a catalytically relevant Mg2+ complexed in the active site of 2,3-dihydroxybenoic acid decarboxylase from Aspergillus oryzae (2,3-DHBD_Ao). This unique example with respect to the nature of the metal is in contrast to mechanistically related decarboxylases, which generally have Zn2+ or Mn2+ as the catalytically active metal.

Reactive crystallization: a review

Reactive crystallization is not new, but there has been recent growth in its use as a means of improving performance and sustainability of industrial processes.

2,3-Dihydroxybenzoic Acid Decarboxylase from Fusarium oxysporum: Crystal Structures and Substrate Recognition Mechanism

A 2,3-dihydroxybenzoic acid decarboxylase from Fusarium oxysporum (2,3-DHBD_Fo) has a relatively high catalytic efficiency for the decarboxylation of 2,3-dihydroxybenzoic acid (DHBA) and carboxylation of catechol, thus it has a different substrate spectrum from other benzoic acid decarboxylases. We have determined the structures of 2,3-DHBD_Fo in its apo form and complexes with catechol or 2,5-dihydroxybenzoic acid at 1.55, 1.97, and 2.45 Å resolution, respectively. The crystal structures of 2,3-DHBD_Fo show that the enzyme exists as a homotetramer, and each active center has a Zn²⁺ ion coordinated by E8, H167, D291 and three water molecules. This is different from 2,6-DHBD from Rhizobium sporomusa, in which the Zn²⁺ ion is also coordinated with H10. Surprisingly, mutation of A10 of 2,3-DHBD_Fo to His resulted in almost complete loss of the enzyme activity. Enzyme-substrate docking and site-directed mutation studies indicate that residue R233^Δ interacts with the 3-hydroxy group of 2,3-DHBA, and plays an important role in substrate recognition for this enzyme, thus revealing the molecular basis 2,3-dihydroxybenzoic acid decarboxylase.

Kolbe-Schmitt type reaction under ambient conditions mediated by an organic base

The combined use of an organic base for resorcinols realized a Kolbe-Schmitt type reaction under ambient conditions. When resorcinols (3-hydroxyphenol derivatives) were treated with DBU under a carbon dioxide atmosphere, nucleophilic addition to carbon dioxide proceeded to afford the corresponding salicylic acid derivatives in high yields.

Non-Oxidative Enzymatic (De)Carboxylation of (Hetero)Aromatics and Acrylic Acid Derivatives

The utilization of carbon dioxide as a C1-building block for the production of valuable chemicals has recently attracted much interest. Whereas chemical CO2 fixation is dominated by C-O and C-N bond forming reactions, the development of novel concepts for the carboxylation of C-nucleophiles, which leads to the formation of carboxylic acids, is highly desired. Beside transition metal catalysis, biocatalysis has emerged as an attractive method for the highly regioselective (de)carboxylation of electron-rich (hetero)aromatics, which has been recently further expanded to include conjugated α,β-unsaturated (acrylic) acid derivatives. Depending on the type of substrate, different classes of enzymes have been explored for (i) the ortho-carboxylation of phenols catalyzed by metal-dependent ortho-benzoic acid decarboxylases and (ii) the side-chain carboxylation of para-hydroxystyrenes mediated by metal-independent phenolic acid decarboxylases. Just recently, the portfolio of bio-carboxylation reactions was complemented by (iii) the para-carboxylation of phenols and the decarboxylation of electron-rich heterocyclic and acrylic acid derivatives mediated by prenylated FMN-dependent decarboxylases, which is the main focus of this review. Bio(de)carboxylation processes proceed under physiological reaction conditions employing bicarbonate or (pressurized) CO2 when running in the energetically uphill carboxylation direction. Aiming to facilitate the application of these enzymes in preparative-scale biotransformations, their catalytic mechanism and substrate scope are analyzed in this review.

Biochemical engineering in China

Chinese biochemical engineering is committed to supporting the chemical and food industries, to advance science and technology frontiers, and to meet major demands of Chinese society and national economic development. This paper reviews the development of biochemical engineering, strategic deployment of these technologies by the government, industrial demand, research progress, and breakthroughs in key technologies in China. Furthermore, the outlook for future developments in biochemical engineering in China is also discussed.

C-H Bond Carboxylation with Carbon Dioxide

Carbon dioxide is a nontoxic, renewable, and abundant C₁ source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chemical transformation of CO₂ with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivatives. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp² )-H bonds of (hetero)arenes, vinylic C(sp² )-H bonds, the ipso-C(sp² )-H bonds of the diazo group, aldehyde C(sp² )-H bonds, α-C(sp³ )-H bonds of the carbonyl group, γ-C(sp³ )-H bonds of the carbonyl group, C(sp³ )-H bonds adjacent to nitrogen atoms, C(sp³ )-H bonds of o-alkyl phenyl ketones, allylic C(sp³ )-H bonds, C(sp³ )-H bonds of methane, and C(sp³ )-H bonds of halogenated aliphatic hydrocarbons. In addition, multicomponent reactions, tandem reactions, and key theoretical studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochemical, and light-driven methods are highlighted.

Carboxylation of Hydroxyaromatic Compounds with HCO3− by Enzyme Catalysis: Recent Advances Open the Perspective for Valorization of Lignin-Derived Aromatics

This review focuses on recent advances in the field of enzymatic carboxylation reactions of hydroxyaromatic compounds using HCO3− (as a CO2 source) to produce hydroxybenzoic and other phenolic acids in mild conditions with high selectivity and moderate to excellent yield. Nature offers an extensive portfolio of enzymes catalysing reversible decarboxylation of hydroxyaromatic acids, whose equilibrium can be pushed towards the side of the carboxylated products. Extensive structural and mutagenesis studies have allowed recent advances in the understanding of the reaction mechanism of decarboxylase enzymes, ultimately enabling an improved yield and expansion of the scope of the reaction. The topic is of particular relevance today as the scope of the carboxylation reactions can be extended to include lignin-related compounds in view of developing lignin biorefinery technology.

Biochemical characterization and substrate profiling of a reversible 2,3-dihydroxybenzoic acid decarboxylase for biocatalytic Kolbe-Schmitt reaction

Reversible benzoic acid decarboxylases are versatile biocatalysts by taking advantage of both decarboxylation and carboxylation reactions, especially for the biocatalytic Kolbe-Schmitt reaction. In the course of developing a benzoic acid decarboxylase tool-box, a putative benzoic acid decarboxylase gene from Fusarium oxysporum was heterologously over-expressed in Escherichia coli, the recombinant protein was purified and characterized. The purified enzyme exhibited relatively high catalytic efficiencies for the decarboxylation of 2, 3-dihydroxybenzoic acid and carboxylation of catechol (k_cat/K_m = 2.03 × 10² and 1.88 mM^-1 min^-1, respectively), and thus characterized as 2, 3-dihydroxybenzoic acid decarboxylase (2, 3-DHBD_Fo). The enzyme also catalyzed the decarboxylation of various substituted salicylic acids with different groups at varied positions except 5-position and the carboxylation of phenol and the substituted phenols. In a preparative reaction, catechol was carboxylated into 2, 3-dihydroxybenoic acid with 95% conversion by adding dodecyldimethylbenzylammonium chloride into the reaction system, and the product was isolated in 72% yield. These results demonstrate that 2, 3-DHBD_Fo is a valuable addition to the benzoic acid decarboxylase tool-box with potential practical applications.

Mechanism and Structure of γ-Resorcylate Decarboxylase

γ-Resorcylate decarboxylase (γ-RSD) has evolved to catalyze the reversible decarboxylation of 2,6-dihydroxybenzoate to resorcinol in a nonoxidative fashion. This enzyme is of significant interest because of its potential for the production of γ-resorcylate and other benzoic acid derivatives under environmentally sustainable conditions. Kinetic constants for the decarboxylation of 2,6-dihydroxybenzoate catalyzed by γ-RSD from Polaromonas sp. JS666 are reported, and the enzyme is shown to be active with 2,3-dihydroxybenzoate, 2,4,6-trihydroxybenzoate, and 2,6-dihydroxy-4-methylbenzoate. The three-dimensional structure of γ-RSD with the inhibitor 2-nitroresorcinol (2-NR) bound in the active site is reported. 2-NR is directly ligated to a Mn²⁺ bound in the active site, and the nitro substituent of the inhibitor is tilted significantly from the plane of the phenyl ring. The inhibitor exhibits a binding mode different from that of the substrate bound in the previously determined structure of γ-RSD from Rhizobium sp. MTP-10005. On the basis of the crystal structure of the enzyme from Polaromonas sp. JS666, complementary density functional calculations were performed to investigate the reaction mechanism. In the proposed reaction mechanism, γ-RSD binds 2,6-dihydroxybenzoate by direct coordination of the active site manganese ion to the carboxylate anion of the substrate and one of the adjacent phenolic oxygens. The enzyme subsequently catalyzes the transfer of a proton to C1 of γ-resorcylate prior to the actual decarboxylation step. The reaction mechanism proposed previously, based on the structure of γ-RSD from Rhizobium sp. MTP-10005, is shown to be associated with high energies and thus less likely to be correct.

Amine-Mediated Enzymatic Carboxylation of Phenols Using CO2 as Substrate Increases Equilibrium Conversions and Reaction Rates

A variety of strategies is applied to alleviate thermodynamic and kinetic limitations in biocatalytic carboxylation of metabolites in vivo. A key feature to consider in enzymatic carboxylations is the nature of the cosubstrate: CO₂ or its hydrated form, bicarbonate. The substrate binding and activation mechanism determine what the actual carboxylation agent is. Dihydroxybenzoic acid (de)carboxylases catalyze the reversible regio-selective ortho-(de)carboxylation of phenolics. These enzymes have attracted considerable attention in the last 10 years due to their potential in substituting harsh conditions typical of chemical carboxylations (100-200 °C, 5-100 bar) with, ideally, greener ones (20-40 °C, 1 bar). They are reported to use bicarbonate as substrate, needed in large excess to overcome thermodynamic and kinetic limitations. Therefore, CO₂ can be used as substrate by these enzymes only if it is converted into bicarbonate in situ. In this contribution, we report the simultaneous amine-mediated conversion of CO₂ into bicarbonate and the ortho-carboxylation of different phenolic molecules catalyzed by 2,3-dihydroxybenzoic acid (de)carboxylase from Aspergillus oryzae. Our results show that under the newly developed conditions a significant thermodynamic (up to twofold increase in conversion) and kinetic improvement (up to approx. fivefold increase in rate) of the biocatalytic carboxylation of catechol is achieved.

Synthesis of Carboxylic Acids and Esters from CO2

The achievements in the synthesis of carboxylic acids and esters from CO₂ have been summarized and discussed.